We’ve probably all made at least one of these bloopers when we’ve exercised. Sometimes we’ve learned the hard way. If you’re just getting going with your fitness plan, be sure to remember these mistakes you can avoid! 1 Exercising too hard or too fast. If you exercise for 30 minutes most days, increase speed and distance by no more than 10% per week. 2  Lack of variety. Doing the same workout month after month can lead to fitness plateaus, boredom and overuse strain or injury. Mix up your activities. 3  Doing all or nothing. Not having a full 30–60 minutes to exercise is no reason to skip your workout. Even 10 minutes of exercise is beneficial. 4  Unrealistic goals. Impractical goals often lead to exercise dropout, if not injury. Stick to a plan that suits you—challenging but not so difficult you get discouraged from lack of progress. 5  Not warming up.